1. Field of the Invention
The present invention relates to a liquid discharge head that discharges droplets of ink or the like for recording on a recording medium and a method of making the liquid discharge head.
2. Description of the Related Art
Inkjet type printers (inkjet printers) are used to form an image by discharging liquid, such as ink, from a liquid discharge head onto a recording medium. The inkjet printers have various advantages, e.g., easier high-definition image formation, higher speed recording, better quietness, and lower price than other types of printer.
Such inkjet printers each include a liquid discharge head that has a plurality of discharge ports, through which ink is discharged, arrayed in a discharge port surface of the head. Many of the discharge port surfaces are subjected to water-repellent treatment. The water-repellent treatment performed on the discharge port surface prevents uneven deposition of ink around the discharge ports. This reduces unintended directional discharge of ink drawn to deposited ink around the discharge ports when ink is discharged.
Instead of the water-repellent treatment, hydrophilic treatment may be performed in the use of an ink that interferes with the effectiveness of water-repellent treatment on the discharge port surface, for example, pigment ink or high-function ink, or in the use of small-diameter discharge ports which tend to increase the viscosity of ink in the discharge ports. Japanese Patent Laid-Open Nos. 8-118656 and 2001-105599 each disclose a liquid discharge head having a discharge port surface subjected to hydrophilic treatment.
The hydrophilic treatment allows a thin layer of ink absorbed by a hydrophilic treatment layer to be formed on the entire discharge port surface, causing little or no difference in wettability between this thin layer and ink deposited around the discharge ports. This allows ink to be easily discharged in an intended direction. Furthermore, the thin layer of ink on the discharge port surface protects ink in the small-diameter discharge ports against drying. This eliminates auxiliary discharge that is needed to discharge high-viscosity ink from a liquid discharge head having a discharge port surface subjected to water-repellent treatment. In addition, since a thin ink layer is formed on the entire discharge port surface during discharge of ink, high ink discharge performance can be stably maintained.
An uneven central region where the discharge ports are arrayed in the discharge port surface of the liquid discharge head leads to nonuniformity in the distance between each discharge port and an energy generating element (ink discharge energy generating element substrate) that causes film boiling of ink. This results in nonuniformity in the volume of ink stored between the discharge port and the energy generating element, thus leading to nonuniformity in the volume of ink to be discharged. Japanese Patent Laid-Open No. 10-157150 discloses a liquid discharge head which has a groove surrounding a plurality of discharge ports like those illustrated in FIG. 9A to provide an even central region, where the discharge ports are arrayed, of a discharge port surface. As regards a liquid discharge head having no groove, resin constituting a resin coating layer spreads out from an applied position by the gravity before the resin coating layer applied on a substrate is cured, resulting in an uneven discharge port surface. In the liquid discharge head disclosed in Japanese Patent Laid-Open No. 10-157150, resin constituting a resin coating layer is applied to an area including a pattern (base pattern) for the groove disposed in the discharge port surface. The pattern for the groove can prevent the resin constituting the resin coating layer from spreading out. This allows a central region of the discharge port surface where the discharge ports are arrayed, specifically, the region inside the groove to become even.
Inkjet printers have recently offered higher image quality and higher speed recording. Achieving these advantages requires smaller droplets of ink discharged and a reduction in ink discharge interval (discharge frequency). In a liquid discharge head which discharges such small droplets at high speed, an increased refill speed, at which a discharge port is refilled with ink, may increase meniscus vibration, thus causing ink to flow over meniscus formed in the discharge port from the discharge port onto a discharge port surface. If the discharge port surface is provided with a hydrophilic treatment layer, the ink which has overflowed onto the discharge port surface is absorbed by the hydrophilic treatment layer, thus forming a thin layer of ink.
In a liquid discharge head having a discharge port array density of 600 dpi or more and an ink discharge frequency of 10 kHz or more, the volume of ink overflowing from discharge ports onto a discharge port surface is too much. Unfortunately, the ink cannot be completely absorbed by a hydrophilic treatment layer. In the liquid discharge head disclosed in Japanese Patent Laid-Open No. 8-118656 or 2001-105599, if ink which has overflowed from the discharge ports onto the discharge port surface is not completely absorbed by the hydrophilic treatment layer, the discharge ports may be blocked by the ink which has not been absorbed. This may inhibit ink from being discharged from the discharge ports.
The liquid discharge head disclosed in Japanese Patent Laid-Open No. 10-157150 has a phenomenon (pinning effect) in which right-angled edges of the groove disposed in the discharge port surface prevent ink from traveling, so that ink does not flow into the groove. A large volume of ink accordingly tends to accumulate due to overflow in the central region surrounded by the groove. Unfortunately, the discharge ports tend to be blocked by ink which has not been absorbed, so that ink may fail to be discharged from the discharge ports.